After upgrading to OpenRoads/OpenRail/OpenSite v10.07.03.18, the program is extremely slow loading cell libraries, or running a command that accesses cells, or loading DGNLIBS that contain a large number of cells.
To resolve this issue, download and install the "Bentley Civil 10.07.03.18 Product Update" here:https://communities.bentley.com/products/road___site_design/m/road_and_site_design_gallery/274013/download
This Civil Product Update provides a fix for slow performance during attachment and use with large cell libraries. This occurs when large cell libraries(DGNLIBs) are directly attached or configured by the workspace/workset configuration. This will be automatically applied to version 10.07.03.18 of OpenRoads Designer, OpenSite Designer, and OpenRail Designer. If any of the prementioned 10.07.03.18 products are installed after this update, a repair can be run to include this update to the newly installed products. The update will appear as "Bentley Civil 10.7.3.18 Product Update" in the Windows list of Programs and Features.